1. Field of the Invention
The present invention relates to a method for driving a gas-discharge panel such as a plasma display panel (PDP) or a plasma addressed liquid crystal (PALC), and a display device using the gas-discharge panel.
A plasma display panel is coming into wide use as a large screen display device for a television set taking advantage of commercialization of color display. Along with the expansion of the market, requirement for reliability of operation has become more rigorous.
2. Description of the Prior Art
As a color display device, an AC type plasma display panel having three-electrode surface discharging structure is commercialized. This device has a pair of main electrodes for sustaining discharge disposed for each row of matrix display, and an address electrode for each column. Diaphragms for suppressing discharge interference between cells are disposed like a stripe. A discharge space is continuous over the entire length of each column. This AC type plasma display panel utilizes a memory function performed by wall charge on a dielectric layer covering the main electrodes on occasion of displaying. Namely, one pair of main electrodes is assigned to a scanning electrode and the address electrode is assigned to a data electrode for addressing by a line-sequential format for controlling the charging state of each cell corresponding to the display contents. After that, a sustaining voltage (Vs) having alternating polarities is applied to all pairs of the main electrodes simultaneously. Thus, a cell voltage (Vc) that is a sum of the wall voltage (Vw) and the applied voltage can exceeds a discharge starting voltage (Vf) only in a cell having a wall discharge above a predetermined quantity, so that the surface discharge occurs along the surface of the substrate for each application of the sustaining voltage. By shortening the period of applying the sustaining voltage, continuous displaying state can be observed.
Concerning a display of sequential images like a television, the addressing and the sustaining are repeated. In general, in order to prevent fluctuations of the display, preparation of addressing is performed for making the charged state uniform over the entire screen, after sustaining of an image and before addressing of the next image.
In the conventional addressing, the charged quantity of the wall charge (wall voltage) is altered by generating the addressing discharge in either the cell to be lighted or the cell not to be lighted. In the writing address format, the wall charge remaining in the display screen is erased as preparation for addressing, and the addressing discharge is generated only in the cell to be lighted, so that an adequate quantity of wall charge is generated in the cell. In the erasing address format, an adequate quantity of wall charge is generated in all cells as preparation of addressing, and then the addressing discharge is generated only in the cell not to be lighted, so that the wall charge in the relevant cell is erased.
In the above-mentioned line-sequential addressing, the charge that contributes to the priming effect helping the addressing discharge occur easily is a space charge remaining after generated by the discharge for the preparation of addressing and a space charge generated by addressing discharge in the cell in the upstream side of the row selection (scanning). However, if the cell in the upstream side is not required to generate the addressing discharge (like a cell not to be lighted in the write addressing format), only the space charge remaining after generated at the stage of the preparation for addressing can contribute to the priming effect since the addressing discharge is not generated in the upstream side. Since the space charge decreases along with time passing, the remaining quantity of the space charge will be smaller, as the addressing is coming to an end, so that delay of discharging becomes larger. For this reason, in a cell of a row that is selected at relatively late timing, there was a case where the addressing discharge cannot occur within the row selection period (scanning period for one row) defined by a scan pulse width, resulting in a display defect. An example of the display defect is a xe2x80x9cblack noisexe2x80x9d in which a part or a whole of the upper edge of a belt cannot be lighted, when the belt is displayed in the lower portion of the screen that is scanned vertically. Especially, in the structure in which the discharge space is defined by a diaphragm having a stripe pattern for each column, movement of the space charge generating the priming effect can occur only in each column, resulting in a display defect.
A method for improving the above-mentioned problem is proposed in Japanese Unexamined Patent Publication 9-6280(A), in which a priming discharge for forming the space charge is generated in the row to be selected before applying the scanning pulse that selects the row. The priming discharge is generated in all cells of the row regardless of the display contents, so that the addressing discharge almost surely occurs.
However, in the conventional driving method, since a priming pulse for generating the priming discharge is applied to the next row to be selected at the same time as application of the scanning pulse to the selected row, it is difficult to optimize the pulse width and the peak value, so that the control becomes complicated. In addition, since the pulse width should be set to a little larger for ensuring generation of the priming discharge, the priming pulse should be applied for each row, and the time necessary for the addressing becomes longer. If the timing for applying the pulse is shifted between rows, the row selection period becomes a sum of the priming pulse width and the scanning pulse width, so that the time necessary for the addressing becomes even longer.
The object of the present invention is to improve the reliability of the addressing while suppressing enlargement of the time necessary for the addressing.
In the present invention, while addressing for controlling the state of the cell in accordance with the state setting data such as display data, it is not selected whether the addressing discharge exists or not, but the quantity of addressing discharge (movement of the electric charge). Namely, a voltage sufficient for generating addressing discharge above the minimum value regardless of the display contents is applied to all of the cells to be addressed. The intensity of the electric discharge depends on the applied voltage.
For example, when the line-sequential addressing is adopted, the space charge that contributes to the priming effect in the row that will be selected next is generated in all of the cells included in the selected row. Therefore, the addressing discharge can be certainly generated for any display pattern by performing the row selection in the order that makes the distance between the nth selected row and the (n+1)th selected row within a predetermined range so that the space charge generated by the addressing discharge becomes effective. If the scanning pulse width is shortened in accordance with increase of the probability of the addressing discharge, the display can be speed up.
The wall voltage can be varied by the addressing discharge in the addressing of the gas-discharge panel in which each cell is charged by the wall charge. Therefore, the wall voltage (the target value) before change is set so that the wall voltage after change becomes the desired value.
FIGS. 1A and 1B show the change in the wall voltage in the addressing of the AC type plasma display panel to which the present invention is applied.
The variation of the wall voltage can be adjusted by setting the intensity of the discharge. However, the variation of the electrode potential will vary either in the direction from a high level to a low level or the opposite direction. Therefore, the combination of lighting or not lighting and the intensity of the discharge includes two patterns as described below.
In the case of writing address format, the wall voltage Vw between main electrodes is set to a value Vw1 within a non-lighting range in which the sustaining discharge cannot be generated as a preprocess of the addressing process. The non-lighting range means a range in which the cell voltage does not exceeds the discharge starting voltage even if the sustaining voltage having the same polarity with the wall voltage Vw is applied. The lower limit of the non-lighting range is the threshold value Vth2 having the negative polarity, and the upper limit of the non-lighting range is the threshold value Vth1 having the positive polarity. In the addressing process, a strong addressing discharge is generated for the selected cell (the cell to be lightened), and the wall voltage Vw is changed to a value in the lighting range in which the sustaining discharge can be generated in the polarity opposite to the previous polarity. In the non-selected cell (the cell not to be lightened), a weak addressing discharge is generated for the priming. In this case, the wall voltage Vw is changed from the value Vw1 into a lower value (zero in the figure).
In the case of erasing address format, the wall voltage Vw between main electrodes is set to a value Vw2 within a lighting range in which the sustaining discharge can be generated as a preprocess of the addressing process. In the addressing process, a strong addressing discharge is generated for the non-selected cell, and the wall voltage Vw is changed from the value Vw2 into a value in the non-lighting range (zero in the figure). In the selected cell, a weak addressing discharge is generated for the priming. In this case, the wall voltage Vw is changed from the value Vw2 into a value Vw2xe2x80x2 in the lighting-range.